Calcium pyrophosphate has been used as an abrasive in dentifrice compositions in the past, but it has rarely been used as the primary abrasive agent because of its extremely high abrasiveness (the radioactive dentin abrasion, RDA, of calcium pyrophosphate can be over 1000 as a 50% aqueous slurry). Instead, calcium pyrophosphate has been usually been added as a secondary polishing agent in compositions based on a primary silica abrasive to increase the abrasiveness of the composition. In addition, like other calcium salts, calcium pyrophosphate suffers from the drawback that in solution it will react with soluble fluoride sources resulting in the precipitation of calcium fluoride. This negatively impacts the composition by removing the fluoride ions that provide important oral care benefits.
Polyphosphates and ionic active ingredients have been used in dentifrices to promote oral health. Polyphosphates are known anti-tartar agents that help retard calculus formation. Metal ions such as stannous and zinc ions are known to be effective anti-microbial agents. These metal ions provide anti-gingivitis and anti-plaque benefits and may also improve breath and reduce tooth or gum sensitivity. Stannous fluoride has been used in dentistry since the 1950's as a fluoride source to prevent dental caries. Similarly, zinc citrate has been shown to have anti-plaque, anti-gingivitis and anti-tartar efficacy. In addition, zinc has also shown efficacy as an anti-malodor agent.
While such actives have previously been used in dentifrices, for several reasons, it has proven challenging to provide these actives together in a stable single phase composition. One such technical problem is to preserve the bioavailability of stannous ions and maximize the chemical stability of the stannous ion source. Many formulations suffer from the problem that the bioavailable levels of stannous and/or zinc drop during aging (e.g., shelf storage). This drop can result in a bioavailable level of stannous and/or zinc as much as 50% less than the formulation quantity. In addition, certain polyphosphates are unstable in high-water aqueous systems. Such polyphosphates in an aqueous system are susceptible to hydrolysis unless they are present at a high pH, which is not compatible with high stannous availability. Stannous fluoride tends to precipitate stannous ions in aqueous environments, thereby reducing the efficacy and availability of the stannous ions in the oral care composition. Additionally, polyphosphates can react with ionic fluoride in oral compositions at ambient temperature to produce monofluorophosphate ions, altering the pH of the composition. This reaction compromises the efficacy of the oral composition and its ability to provide stable ionic fluoride and polyphosphate to the oral surfaces.
Other attempts to provide such efficacious dentifrice compositions have reduced the amount of water present in the composition. Reducing the amount of water would theoretically reduce or eliminate the stability issues associated with the fluoride, polyphosphate and other ionic actives. However, reducing the level of water, and optionally replacing some or all of the removed water with a humectant, creates problems in obtaining acceptable rheology and thickening properties in the composition. When water, which is a highly polar solvent, is removed, conventional thickening agents such as carboxymethylcellulose (“CMC”) tend to inadequately gel up. Attempts to reduce water content in dentifrice compositions have included the dentifrices described in, e.g., EP 0 638 307 B1; U.S. Pat. Nos. 4,647,451; and 5,670,137. Such known formulations have been shown to exhibit progressive thickening over time, which prolongs the time period to reach a rheological steady state, or even prevents the dentifrice from reaching a rheological steady state. Ideally, dentifrice formulations need to reach a steady state for consumer acceptance within two weeks. If a formulation routinely increases in viscosity over time, dispensing of the formulation will become difficult, which will likely result in consumer dissatisfaction.
U.S. Pat. No. 6,696,045 discloses dentifrice compositions comprising a single low water phase comprising polyphosphate and ionic active ingredients. Although compositions comprising glass H polyphosphate, which has a long chain of about 21 phosphate groups, and sodium or stannous fluoride are disclosed, with the sodium fluoride being optionally combined with zinc citrate and the stannous fluoride being optionally combined with zinc lactate, there is no disclosure of how to combine stannous, fluoride and zinc salts in a low water composition in combination with short chain length polyphosphates in a low water single phase system.
Other attempts to provide dentifrice compositions having these actives in efficacious amounts involved the use of dual compartmented packaging wherein the reactive ingredients are physically separated until the time of brushing. (See, e.g., WO98/22079, “Dentifrice Compositions Containing Polyphosphate and Fluoride.”) However, such dual-compartmented packages are typically considerably more expensive than the conventional laminate tubes that have been used for many years to contain and dispense dentifrices. They also may be problematic in terms of ease of consumer use and uniform dispensing of approximately equal amounts of each composition during each consumer use. Another approach that has been used is the encapsulation of the metal ion sources in a polymer matrix, but this adds considerably complexity to the formulation of the composition.